Avoid ePN "unitialized value" error for type 3 checks

Since the help output shows a type 3 check without a provided warning or error user level, reset these to blank for performance status line consistency even if they are provided (since any provided values are ignored).  Setting them here avoids a Nagios embedded Perl interpreter compilation error.
Merge pull request #1 from emsearcy/master

Bugfix for ePN uninitialized use of variable